Ever wonder why a straw or even a plant appears to bend in water or why your legs look weird when you’re standing in a pool? Well, all of this ‘bending’ of the light is actually called refraction, and it’s all behind something known as Snell’s Law. Why this is so vital in everyday life is just what we are going to explore in this article.
What is Snell’s Law?
Snell’s law can let us know how and why the light is going to bend when it travels from one material into another. For example, it would just about be the same thing as running from the dry sand right into the water at the beach-you are slowing down and changing direction a bit. Only this time, we are talking about light in travel.
Why Does Light Bend?
Light can be pretty cool, since it travels at different speeds depending on what it is moving through : it goes really fast in air, it goes more slowly in water, and it goes most slowly in glass. If the light moves from one material into another at an angle, then something funky happens-it bends! We refer to this bending of the light as “refraction.”
It might be easier to understand why this occurs if one imagines light as a wave. Thus, when this wave moves from the air into the water, for example, part of it slows down first while the other part is still speeding along. This speed difference makes the whole wave change direction-that’s the bending we see. You see this in real life! If you shine a flashlight at an angle into a fish tank, that beam of light will bend as it enters the water. It also is why things in water at times can appear wavy or bent; this is because light slows down and it changes direction when it moves between different materials.
The Law in Action
Snell’s Law gives us a way to predict how much the light will bend. The formula is: n1sin(θ1)=n2sin(θ2)
Don’t worry about the math too much! Here’s what it means in simple words:
- n1 and n2 are numbers called “refractive indices.” One of them can be called as incident index while the other can be called refractive index. They tell us how fast light travels in each material.
- θ1 is the angle the light hits the new material (like the angle between the light beam and an imaginary line called the “normal” that stands straight up from the surface).
- θ2 is the angle the light travels in the new material after it bends.
Understanding Refractive Indices
Refractive indices are the important parameters between the behaviors of light in different materials. They are just numbers showing the degree a particular material can bend light. For example, the refractive index of air is approximately 1, that of water is about 1.33, and that of glass can be about 1.5. The higher the refractive index, the more the light is slowed down and bent upon entry into that material. Picture the following: You are on a skateboard, moving on a smooth path, then suddenly on thick grass. In that case, you would be slowed down, and if you didn’t run straight on it, you would change direction, too. And that is what happens to light when it hits a new material at an angle. Part of the skateboard that reaches the grass first actually slows down, and thus it twists. Similarly, the portion of the light wave that first reaches the new medium is itself slowed which thereby bends the light.
If you want to calculate one of the parameters in Snell’s law, you can use the calculator below. Just enter any three of the four values-indices of refraction n₁ and n₂ and the incident and refracted angles, θ₁ and θ₂-and click “Calculate” to return the value of the fourth. If you want to calculate other photonics formulae, you may visit our photonics calculators. The calculators can calculate from laser spot size to peak power, decibel to percentage, frequency to wavelength, etc.
Snell’s law calculator – add 3 of 4 value given in the calculator to calculate the 4th one.
Why is Snell’s law Important?
Knowledge of Snell’s Law has enabled us to develop such magnificent devices as lenses for eyeglasses and cameras. It explains to the scientist how different materials take light, knowledge quite essential while making anything from a microscope to a telescope. It is not possible to design such precise lenses required by these devices without Snell’s Law.
Snell’s law is important for many real-life examples. For example, glasses and contact lenses are applied in order to correct vision by bending light rays using Snell’s law, which focuses them properly on the retina. Cameras work in the same way while focusing images on a film or even sensors. Microscopic lenses and lenses of a telescope do the same thing, bending light, which allows us to see tiny details of an object being studied, or even look at stars that are quite far away from us. Apart from all these, light and its behaviour contribute significantly in our world in every possible field, starting from art and photography to science and technology. Using the principles of light and refraction, photographers create amazing effects; similarly, artists capture great images in unique ways.
Scientists investigate the properties of light to understand properties of materials, atoms, and molecules. These studies have enabled quantum mechanics, laser physics, and spectroscopy. The propagation of light through the atmosphere allows us to investigate weather patterns and climate change and to understand the depletion and recovery of the Earth’s ozone layer.
In addition to refraction, Snell’s Law predicts another phenomenon called total internal reflection. It occurs when light attempts to pass, at a steep angle, out of a medium that has a greater refractive index into one with a lower refractive index-from water into the air, for example. Rather than being transmitted, the light is reflected within the original material. That is the working principle of fibre optics, where light signals are confined within glass made of fibres that can enable the transmission of data over a very long distance with a minimal loss. Without Snell’s law, we wouldn’t have been using the internet and telecommunication technology that we use today.
This is the principle behind fiber optics, where light signals are kept within glass made of fibers, allowing data to be transmitted over long distances with minimal loss. Without Snell’s Law, we wouldn’t have the internet and telecommunications technology we rely on today.
See Snell’s Law in Action
You can see Snell’s Law in action by conducting an easy experiment at home. Just fill the glass with water full. Then place a straw in a glass and view it from the side. The straw will appear to bend at the point where it enters the water; that’s the refraction in action! You can further observe this by sending a laser beam through a laser pointer into the water at various angles to see how the light beam bends.
Conclusion
Among the general principles that can explain the bending of light in passing from one medium to another, Snell’s Law holds the lead. While an understanding of this law can help anyone predict and control the behavior of light in several applications-from lens design to more advanced technologies-these simple tricks just would not be seen without the explanation afforded by Snell’s Law.
Did you know?
– Although Snell’s Law is named after Dutch mathematician Willebrord Snellius, the law was known to physicist Ibn Sahl in 984 AD, long before Snellius [1].
– Despite Ibn Sahl’s earlier formulation, Descartes independently derived the law in 1637 and published it, leading to its widespread recognition in the Western scientific community.
– Snell’s Law is that it not only applies to light passing through different materials but also to other wave phenomena, such as sound waves traveling through varying mediums like air and water [2].
– It finds application in areas like seismology, where it helps determine how seismic waves refract as they travel through different layers of the Earth’s crust, aiding in understanding geological structures [3].
References
[1] Rashed, R., A Pioneer in Anaclastics: Ibn Sahl on Burning Mirrors and Lenses. Isis, 81(3), 464-491 (1990).
[2] Born, M., & Wolf, E., Principles of Optics: Electromagnetic Theory of Propagation, Interference and Diffraction of Light (7th ed.). Cambridge University Press, (1999).
[3] Shearer, P. M., Introduction to Seismology (2nd ed.). Cambridge University Press (2009).
